1. Field of Invention
The present invention relates to broadband wireless access systems and, among other things, to a programmable PHY for use in broadband wireless access systems.
2. Discussion of Background
Point to multi-point fixed broadband wireless access systems over Multichannel Multipoint Distribution System (MMDS) networks are known in broadcast situations. These networks operate over licensed bands including the MMDS band (2,150 to 2,162 MHz), the Wireless Communication System (WCS) band (2,305 to 2,311 MHz) and the Institutional Television Fixed Service/Multichannel Multipoint Distribution System (ITFS/MMDS) bands (2,500 to 2,686 MHz).
A known wireless broadband access system, which operates at a range of between 50 MHz and 864 MHz, but not in the MMDS, WCS, or ITFS/MMDS bands, is the data over cable specification system, which is specified in the data over cable system interface specifications (DOCSIS). An overview of a wireless DOCSIS system is depicted in FIG. 1. A Cable Modem Termination System (CMTS) 10 communicates with a wide area network 20, such as the Internet. The CMTS 10 can transmit signals from the wide area network 20 along a cable network 30 through cable modems 40 to Customer Premise Equipment (CPE) 50. CPE 50 messages can be transmitted to the wide area network 20 through the cable modem 40 along the cable network 30 to the CMTS 10.
In point to multi-point broadband wireless access systems one central end-point, e.g. the head-end, communicates through a bi-directional link or links with multiple end-points, e.g. the nodes. The number of nodes in communication varies in time and can be none, one or two or more at any specific time.
The link(s) between the head-end and the nodes are combined in one or more channels. The signal path from the central end-point to the nodes is referred to as downstream, while the signal path from the nodes to the central end-point is referred to as upstream.
A single upstream channel can be used to deliver information from a node to the head-end and downstream channels are used from the head-end to a node or a group of nodes. If a single upstream channel is used for communication from the nodes(s) to the central point, then only one end-point can sends information on the single upstream channel at any one time.
Additionally, in such a system the diverse topological conditions of each user within the service area in terms of factors such as signal to noise, multi-path and fading makes it difficult to implement a flexible communication scheme that will enable per user optimization with respect to robustness and throughput.